Atomic Weights For Ten Elements Refined

It is neat that we can still refine themensuration used for atomic weight on the periodic table for these ten elements.  They all have an isotopic history that isaffected for external factors enough to introduce a lot of uncertainty.

In a couple of years you will be justified ingetting an up to date periodic table, though that has been common place enoughif one was in the habit of adding transuranic elements as they emerged from thelaboratories.

That this was needed was obvious for sometime.  It is likely the methodology hassimply improved to the point that it is good enough to do the job for a longtime.

Atomicweights of 10 elements on periodic table about to make an historic change

December15, 2010

MichaelWieser is a scientist from the University of Calgary who is helpingto update periodic table. Credit: Riley Brandt/University of Calgary

For the first time in history, achange will be made to the atomic weights of some elements listed on the Periodictable of the chemical elements posted on walls of chemistry classrooms and onthe inside covers of chemistry textbooks worldwide.

The newtable, outlined in a report released this month, will express atomic weights of10 elements: 

hydrogen, lithium, boron, carbon, nitrogen, oxygen,silicon, sulfur, chlorine, and thallium

in a new manner that will reflectmore accurately how these elements are found in nature.

"Formore than a century and a half, many were taught to use standard atomic weights— a single value — found on the inside cover of chemistry textbooks and on the periodictable of the elements. As technology improved, we havediscovered that the numbers on our chart are not as static as we havepreviously believed," says Dr. Michael Wieser, an associate professor atthe University of Calgary, who serves as secretary of the International Unionof Pure and Applied Chemistry's (IUPAC) Commission on Isotopic Abundances andAtomic Weights. This organization oversees the evaluation and dissemination ofatomic-weight values.

Modernanalytical techniques can measure the atomic weight of many elements precisely,and these small variations in an element's atomic weight are important inresearch and industry. For example, precise measurements of the abundances of isotopesof carbon can be used to determine purity and source of food, such as vanillaand honey. Isotopic measurements of nitrogen, chlorine and other elements areused for tracing pollutants in streams and groundwater. In sports dopinginvestigations, performance-enhancing testosterone can be identified in thehuman body because the atomic weight of carbon in natural human testosterone ishigher than that in pharmaceutical testosterone. 

Theatomic weights of these 10 elements now will be expressed as intervals, havingupper and lower bounds, reflected to more accurately convey this variation inatomic weight. The changes to be made to the Table of Standard Atomic Weightshave been published in Pure and Applied Chemistry anda companion article in Chemistry International.

Forexample, sulfur is commonly known to have a standard atomic weight of 32.065.However, its actual atomic weight can be anywhere between 32.059 and 32.076,depending on where the element is found. "In other words, knowing theatomic weight can be used to decode the origins and the history of a particularelement in nature," says Wieser who co-authored the report.

MichaelWieser, a professor at the University of Calgary, is contributing to changes tothe periodic table. He works with a thermal ionization mass spectrometer usedto measure the isotope abundance of an element. Credit: Riley Brandt/Universityof Calgary

Elementswith only one stable isotope do not exhibit variations in their atomic weights.For example, the standard atomic weights for fluorine, aluminum, sodium andgold are constant, and their values are known to better than six decimalplaces.

"Thoughthis change offers significant benefits in the understanding of chemistry, onecan imagine the challenge now to educators and students who will have to selecta single value out of an interval when doing chemistry calculations," saysDr. Fabienne Meyers, associate director of IUPAC.

"Wehope that chemists and educators will take this challenge as a uniqueopportunity to encourage the interest of young people in chemistry and generateenthusiasm for the creative future of chemistry."

The University of Calgary has and continues to contributesubstantially in the study of atomic weight variations. Professor H. Roy Krousecreated the Stable Isotope Laboratory in the Department of Physics andAstronomy in 1971. Early work by Krouse established the wide natural range inthe atomic weight of significant elements including carbon and sulfur.Currently, researchers at the University of Calgary in physics,environmental science, chemistry and geoscience are exploiting variations inatomic weights to elucidate the origins of meteorites, to determine sources ofpollutants to air and water, and to study the fate of injected carbon dioxidein geological media.

Thisfundamental change in the presentation of the atomic weights is based upon workbetween 1985 and 2010 supported by IUPAC, the University of Calgaryand other contributing Commission members and institutions.

Providedby University of Calgary (news : web)

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